Question: Why is Blasting necessary?
Answer: In any kind of construction, quarrying or mining operation, blasting is generally considered the quickest and least costly method of removing rock. If explosives could not be used, many projects would become unreasonably expensive and would simply not be built. Blasting makes it possible for all of us to have new highways, transportation systems, and improved utilities. It allows for residential development to provide housing and commercial development to provide jobs. And blasting results in more affordable consumer prices for coal and other products that come from rocks and minerals.
Question: How close can they blast to my house?
Answer: In all surface mining operations, no blasting shall be done within 300 feet of any home unless approved in writing by the property owner. There are no distance limitations governing construction blasting. However, airblast and ground vibration limits may not exceed state standards regardless of distance from the blast.
Question: If dishes rattle, is my house being damaged?
Answer: Homeowners should not be surprised that even when blast vibration levels are far below the legal limit, highly perceptible vibration can be experienced inside the home; windows and dishes might rattle, knickknacks and pictures might move or fall if not securely fastened, and swag lamps or chandeliers might sway. These effects can be generated by ground vibration or airblast acting separately or together, and can last from one to three seconds or more depending upon the distance from the blast, geologic influences and other factors. Despite these sometimes startling effects, there is absolutely no correlation between how a blast "feels" and its potential for causing structural damage to a home. In fact, cultural stresses (e.g., doors slamming, kids jumping, people ascending or descending stairs) and natural stresses (e.g., sunlight, wind, rain, temperature and humidity fluctuations and changes in soil moisture) place greater stresses on a home than legal blast vibrations.
Question: How will blasting effect my water well?
Answer: Blastholes are normally drilled vertically and arranged in a grid pattern. Typical blasthole diameters range from two to seven inches in quarries and five to nine inches in surface coal mines, with typical depths from 10 to 70 feet. Upon detonation, fracturing of rock generally occurs not greater than 20 to 30 feet from any blasthole, depending largely upon hole diameter and the densities of the rock and explosive. A common misconception is that fracturing extends far beyond the mine property - even miles from the blast site. If this were true, the blastholes could be placed much farther apart than the commonly used spacing of six to 18 feet in quarries and 12 to 25 feet in surface coal mines, and blasting would be much more economical since less drilling and explosives would be necessary.
Question: What is a pre-blast survey?
Answer: A pre-blast survey will document the conditions of the structure, and record any pre-blasting damage and other physical factors that could reasonably be affected by blasting on the proposed permit. A sample of the dwellings water supply shall be taken to account the quality and quantity of the supply. Copies of the completed survey will be supplied to the resident or owner of the structure, the Bureau of Mining and Reclamation and the operator conducting the survey. Pre-blast surveys are conducted by an independent company at the expense of the operator.
Question: What are my rights concerning pre-blast surveys?
Answer: The Department requires before any blasting is approved:
1. All bituminous surface coal operators to notify all
residents within 1/2 mile of blasting site, of
their rights to obtain a pre-blast survey.
2. All industrial mineral operators (quarries)
seismograph all shots and design for .5 in/sec. or
less or notify all residents within 1000 feet of
the blasting site of their rights to obtain
3. Anthracite surface coal mines and construction
operators are not required to offer pre-blast
surveys unless specified by permit condition or
Question: What causes ground vibration and how is it measured?
Answer: When a blast is detonated, some the explosive energy not utilized in breaking rock travels through the ground in all directions as wave motion, similar to the ripple created in a pond when a stone hits the water. This wave motion, or ground vibration as it is commonly called, travels mainly along the surface at speeds of 5,000 to 20,000 feet per second, depending upon the density and thickness of the rock and the soil. Its energy level decreases rapidly with distance from the blast and normally decays to levels undetectable by humans beyond a few thousand feet. Because explosives are expensive and vibration represents wasted energy, it is to the blaster's advantage to utilize as much of the energy as possible in fragmentation, thereby minimizing vibration. Blasting seismographs are used to measure ground vibration in terms of particle velocity, which is the speed at which each particle in the ground oscillates as the wave motion passes. This would be similar to measuring the speed of a fishing bobber in a pond as it moves up and down when a ripple passes under it. Particle velocity is measured in inches per second, but beyond a few hundred feet from a blast the actual movement of the ground, or displacement, is generally only a tiny fraction of an inch, about the thickness of a piece of paper, or less. So it is important to understand that a particle velocity reading expressed in inches per second refers to the speed at which the ground moved, and not the amount of movement.
Blasters control ground vibration mainly by limiting the weight of explosives detonated within any eight-millisecond period of time. They do this by using millisecond delay detonators (blasting caps) to separate the firing time of each hole from adjacent holes. In a typical 50=hole blast, the result would be 50 smaller and separate explosions instead of one large blast. A common misconception is that the number of blastholes determines the resulting intensity of vibration. However, given the same charge-weight per delay (pounds of explosive detonated within an eight-millisecond period) and the same distance, a 100-hole blast can be designed to produce not more vibration than a 10-hole blast.
Question: What is airblast and how is it measured?
Answer: When a blast is detonated, some energy is lost to the atmosphere in the form of noise and/or concession. This phenomenon is caused by the venting of gases through cracks and fissures and the upward and outward movement of the rock on top and in front of the blastholes. The resulting increase in the air pressure is commonly called airblast. Like ground vibration, airblast levels decrease rapidly with the distance from the blast. However, airblast travels only at the speed of sound, around 1,100 feet per second, depending upon air temperature, and can be greater influenced by wind direction and speed, and by atmospheric temperature inversions which can bend it back toward the earth and focus its energy several miles away.
Airblast is usually measured with a special microphone connected to the same type of seismograph that measures ground vibration. The most common units of airblast measurement are pounds per square inch (psi) and the decibel (dB), which is based on a logarithmic sound-pressure scale related to human hearing. The threshold of hearing begins at zero decibels. An increase of six decibels represents a doubling of air pressure. As an example, an airblast measured at 126 dB would have twice the air pressure of an airblast at 120 dB.
Airblast is controlled mainly by the proper use of stemming material (the drill cuttings or crushed stones that are shoveled back into the blasthole after the explosive material has been loaded to a predetermined depth from the surface) and by not loading explosives into portions of holes with cracks, voids or mud seams. These techniques minimize the escape of gases and confine the explosive energy where it is needed to efficiently break rock.
Question: What are the ground vibration and airblast limits?
Answer: The United State Bureau of Mines (USBM) has conducted extensive research during the last three decades on the effects of blast-induced ground vibration and airblast on residential structures. This research produced recommended limits that, if adhered to, will effectively protect residential structures from damage, even if the blasting is repeated on a daily basis over a period of many years.
Pennsylvania's current regulated limits are:
BITUMINOUS COAL MINE 1.0 133 dB
ANTHRACITE 2.0 133 dB
INDUSTRIAL MINERALS (QUARRIES) 2.0 133 dB
CONSTRUCTION 2.0 NONE
The Department of Environmental Protection staff will investigate blasting complaints from the public. Blast reports and seismic data are reviewed for completeness, accuracy, and regulatory compliance. The Department has no authority to require compensation if damage occurs. Compensation for damage is strictly a civil matter between the operator and the landowner. Where a potential for damage may exist, the Department may require modification of the blast plan to reduce vibration levels. If the blast plan has been violated, enforcement action will be taken.
Contact your local DEP District Mining and Reclamation office with any questions or concerns you may have about blasting.
Pottsville District Office 717/621-3118
COUNTIES: ADAMS, BERKS, BUCKS, CARBON, CHESTER, COLUMBIA, DAUPHIN, CUMBERLAND, DELAWARE, FRANKLIN, JUNIATA, MONROE, LEBANON, LEHIGH, LUZERNE, MIFFLIN, MONTGOMERY, PIKE, MONTOUR, NORTHHAMPTON, PERRY, NORTHUMBERLAND, PHILADELPHIA, SCHUYLKILL, SNYDER, SUSQUEHANNA, UNION, WAYNE, WYOMING AND YORK.
Hawk Run District Office 814/342-0410
COUNTIES: BRADFORD, CAMERON, CENTRE, CLEARFIELD, CLINTON, POTTER, LYCOMING, SULLIVAN AND TIOGA.
Greensburg District Office 412-925-5500
COUNTIES: ALLEGHENY, ARMSTRONG, BEAVER, FAYETTE, GREENE, WASHINGTON AND WESTMORELAND.
Ebensburg District Office 814/472-1900
COUNTIES: BEDFORD, BLAIR, CAMBRIA, FULTON, HUNTINGDON, INDIANA AND SOMERSET.
McMurray District Office 412/941-7100
ALL COUNTIES WERE MINING AND SUBSIDENCE OCCUR
Knox District Office 814/797-1191
COUNTIES: BUTLER, CLARION, CRAWFORD, ELK, ERIE, FOREST WARREN, JEFFERSON, LAWRENCE, MCKEAN, MERCER AND VENANGO